1. Field of the Invention
The present invention relates to a method and an apparatus for correcting a resolver output, more particularly to correcting an offset error and a gain error of the resolver output.
2. Description of Related Art
Resolvers are rotational angle sensors that are commonly used for sensing rotational angles of rotary devices, such as engines and vehicular motors. The resolvers have windings for producing magnetic flux linked to the windings. However, an amount of the magnetic flux changes over time, and the resolvers have variations in the amount of the magnetic flux during manufacturing. This results in worsening accuracy of detecting the rotational angle.
In detail, the resolver produces a sine output signal and a cosine output signal. The sine output signal is expressed by an equation, (G+ΔG1)·(sin ωt×sin θ)+(Vb+ΔV1). The cosine output signal is expressed by another equation, (G+ΔG2)·(sin ωt×cos θ)+(Vb+ΔV2).
In the equation, “θ” is a detection angle, “sin ωt” is a carrier wave signal, “G” is a model gain of the resolver (for example, 2.5), and “Vb” is a bias voltage (for example, 2.5 volt). “ΔG1” is a gain variation (deviation) of the sine output signal, “ΔG2” is a gain variation of the cosine output signal, “ΔV1” is an offset variation of the sine output signal, and “ΔV2” is an offset variation of the cosine output signal. Further, the sine output signal and the cosine output signal are produced as analog voltages.
Much expense in time, costs and efforts are required to ensure the accuracy for a long time and to reduce a detection error due to the changes of the gain and the offset. However, an advanced accuracy of the resolver is desired.